In the case of lack of information, how to improve the reliability of the evaluation of the damage effect of multiple missiles against irregular surface targets is a major difficulty in the research of missile operation. An evaluation model for the damage effect on area targets with given parameters was established using the Monte Carlo method. Belief degree distribution functions were employed to assess the uncertainties in the problem, and the assessment results showed a high level of uncertainty in the damage effect. Based on belief entropy, the influence of the uncertainty in each attribute of the missile on the uncertainty of the damage effect was analyzed. By specifically reducing the uncertainty of attributes with significant impact, the uncertainty of the damage effect was iteratively decreased. Simulation results show that the range of uncertainty for the effective damage rate of the area target is significantly reduced. This research can effectively guide the work of damage assessment and reduce its uncertainty.